1. Field of the Invention
The present invention relates to a series of novel volatile noble metal organometallic complexes, and to a method for the preparation thereof. Such complexes are particularly useful as chemical vapor deposition (CVD) precursors for formation of noble metal-containing thin films on substrate assemblies.
2. Description of the Prior Art
Chemical vapor deposition (hereafter indicated as “CVD”) is widely used for the deposition of noble metal-containing thin films on a variety of substrate assemblies. CVD is a particularly attractive method for forming thin film coatings in the semiconductor industries because it has the ability to readily control the composition of the thin film and to form a thin film layer without contamination of, or damage to the substrate assembly. CVD may also be applied to deposit the desired thin film into holes, trenches, and other stepped structures. In situations where conformal thin film deposition is required, CVD would also be a preferred method, since evaporation and sputtering techniques cannot be used to form a conformal thin-film layer. However, CVD processes require suitable source reagents that are sufficiently volatile to permit a rapid transport of their vapors into the CVD reactor. The source reagents, which may be called the precursors, should be relatively stable and inert against oxygen and moisture in air at room temperature to allow long-term storage. They also should decompose cleanly in the CVD reactor to deposit a high purity metal component at the desired growth temperature on the substrate assembly.
The tris-acetylacetonato and tris-allyl iridium(III) complexes Ir(acac)3 and Ir(C3H5)3 are two commonly known CVD precursors, for which the commercially available Ir(acac)3 is a better choice due to its excellent air stability. However the high melting point and low volatility of Ir(acac)3 has limited its development as the industrial standard. In addition, other source reagents consist of Ir(I) metal complexes such as Ir(COD)(MeCp), COD=1,4-cyclooctadiene and MeCp=methylcyclopentadienyl, Ir(COD)(hfac), hfac=hexafluoroacetylacetonate, Ir(COD)(amak), amak=OC(CF3)2CH2NMe2, [Ir(COD)(μ-OMe)]2, [Ir(COD)(μ-OAc)]2, OAc=acetate, and [Ir(CO)2(μ-SBut)]2. For this family of iridium CVD precursors, the monomeric metal complexes Ir(COD)(MeCp) and Ir(COD)(hfac) appear to be more useful for iridium deposition due to their enhanced volatility and vapor phase transport properties which are uncomplicated by monomer-dimer equilibria. The physical properties of these iridium CVD precursors are listed in Table 1.
The chemical vapor deposition of osmium was achieved using the commercially available osmocene (C5H5)2Os, osmium tetraoxide OsO4, or even the metal carbonyl complexes such as Os(CO)5, Os3(CO)12, Os(CO)4(hfb), where hfb=hexafluoro-2-butyne, and the tailor-made precursor complexes Os(CO)4I2, Os(CO)3(tfa)(hfac), tfa=trifluoroacetate, and even [Os(CO)3(hfpz)]2, hfpz=3,5-bis(trifluoromethyl) pyrazolate. Osmium-containing thin films with reasonable purity were obtained in most of these studies; however, the usage of these source reagents has encountered difficulties such as the greater toxicity for OsO4, poor thermal stability for Os(CO)5, and lower gas phase transportation capability for the osmocene complex (C5H5)2Os and polynuclear metal complex Os3(CO)12.
Moreover, the known ruthenium CVD precursor complexes include ruthenocene, Ru(C5H5)2, and its alkyl substituted complexes, such as Ru(C5H4Et)2, carbonyl complexes, such as Ru(CO)4(hfb), hfb=hexafluoro-2-butyne, Ru(CO)2(hfac)2 and Ru3(CO)12; tris-β-diketonate complexes, such as Ru(acac)3, Ru(tfac)3 and Ru(tmhd)3; and organometallic olefin complexes, such as bis(2,4-dimethylpentadienyl)ruthenium, bis(2,4-dimethyloxapentadienyl)ruthenium, Ru(η6-C6H6)(η4-C6H8), C6H8=1,3-cyclohexadiene, and Ru(COD)(C3H5)2, COD=1,5-cyclooctadiene. Selected physical properties of these known osmium and ruthenium organometallic reagents are listed in Table 2.
Accordingly, there is a continuing need for highly volatile and relatively air and thermally stable CVD source reagents for various CVD applications, such as the formation of bottom electrodes, diffusion barriers, conductors, superconductors, dielectrics, capacitors, protective coatings and catalytic metal alloy films. More specifically, the iridium as well as the ruthenium source materials are becoming important for fabricating metallic iridium and ruthenium, iridium oxide (IrO2) and ruthenium oxide (RuO2) that have recently gained interest for use as bottom electrodes in both dynamic random access memories (DRAMs) and for ferroelectric-based memory devices (FRAMs), which incorporate perovskite metal oxides as the capacitor layer. Such perovskite dielectric materials include SBT, BST, PZT, PLZT, etc., wherein SBT=strontium bismuth tantalite, BST=barium strontium titanate, PZT=lead zirconium titanate and PLZT=lead lanthanum zirconium titanate. The practical advantages of iridium and ruthenium based materials over other electrode materials include ease of deposition, good adhesion to Si wafer, the ability to form a stable conducting oxide at high temperatures in an oxidizing environment, and the ability to operate at high temperatures in a working device. On the other hand, osmium CVD source reagents may find application in replacing the relatively less stable source reagent Os(CO)5 or the highly toxic compound OsO4 for making the osmium-coated thermionic cathodes and abrasive-resistant osmium hard-coatings.
Generally speaking, CVD of these metal-containing thin film coatings has been limited due to a variety of reasons, including formation of poor film quality, requiring of high processing temperatures, lack of suitable precursor compounds, and instability of the precursors used in the deposition systems. The availability of suitable precursors with moderate volatility and stability appears to be the greatest limiting factors in the CVD applications, as the poor stability against heat and moisture makes them difficult to store and handle, yields inferior thin film coatings and creates serious contamination at the as-deposited thin films in production-scale operations.
It is therefore an object of the present invention to provide suitable novel CVD precursors that are amenable to use in the chemical vapor deposition of noble metal-containing films.
Based on the need for these noble metal-containing coatings, the prior art has sought to provide new design for the suitable CVD precursors and continued to seek improvements in their basic physical properties that are advantageous for integration with current CVD technology.
It is another object of the present invention is to provide a simplified CVD method for forming a noble metal-containing film on a substrate assembly utilizing these newly prepared precursors. Other objects, features, and advantages will be more fully apparent from the ensuing disclosure and appended claims.
TABLE 1Selected physical properties of known iridium CVD precursorsCompoundM.P. (° C.)CVD TD (° C.)Sublimation ConditionReferencesIr(acac)3300–400° C.subl. at 180–200° C.(a)Ir(C3H5)3dec. at 65° C.100° C.subl. at 50° C./15 torr(b)Ir(COD)(MeCp)38–40° C.270–350° C.subl. at 95° C./0.05 torr(c) and (d)Ir(COD)(hfac)120° C.250–400° C.subl. at 60° C./0.05 torr(e)Ir(COD)(amak)127° C.350° C.subl. at 50° C./0.2 torr(f)[Ir(COD)(μ-135° C.250° C.subl. at 125° C./0.07 torr(c)OAc)]2[Ir(CO)2(μ-SBut)]2128° C.; dec. 160° C.150–450° C.subl. at 80–140° C./0.1 torr(f)Abbreviations:TD = deposition temperature,acac = acetylacetonate,C3H5 = allyl,MeCp = methylcyclopentadienyl,hfac = hexafluoroacetylacetonate,amak = OC(CF3)2CH2NMe2,COD = 1,5-cyclooctadiene,OAc = acetate.(a) Sun, Y.-M.; Endle, J. P.; Smith, K.; Whaley, S.; Mahaffy, R.; Ekerdt, J. G.; White, J. M.; Hance, R. L. Thin Solid Films 1999, 346, 100.(b) Kaesz, H. D.; Williams, R. S.; Hicks, R. F.; Zink, J. I.; Chen, Y.-J.; Muller, H.-J.; Xue, Z.; Xu, D.; Shuh, D. K.; Kim, Y. K. New. J. Chem. 1990, 14, 527.(c) Hoke, J. B.; Stern, E. W.; Murray, H. H. J. Mater. Chem. 1991, 1, 551.(d) Sun, Y.-M.; Yan, X.-M.; Mettlach, N.; Endle, J. P.; Kirsch, P. D.; Ekerdt, J. G.; Madhukar, S.; Hance, R. L.; White, J. M. J. Vac. Sci. Technol. 2000, 18, 10.(e) Xu, C.; Baum, T. H.; Rheingold, A. L. Chem. Mater. 1998, 10, 2329.(f) Chen, Y.-L.; Liu, C.-S.; Chi, Y.; Carty, A. J.; Peng, S.-M.; Lee, G.-H. Chem. Vap. Deposition 2002, 8, 17.(g) Serp, P.; Feurer, R.; Kalck, P.; Gomes, H.; Faria, J. L.; Figueiredo, J. L. Chem. Vap. Deposition 2001, 7, 59.
TABLE 2Relevant physical properties of selective known osmiumand ruthenium CVD precursorsCompoundM.P. (° C.)CVD TD (° C.)Relative volatilityReferencesOsmocene194–198350–500° C.(a)Os3(CO)12226–228° C.225° C.vaporized at 50° C.(b)Os(CO)4(hfb)600° C.subl. at 25° C./0.05 torr(c)Os(CO)4I2450–550° C.subl. at 55° C./0.45 torr(d)Os(CO)3(tfa)(hfac)153–156° C.400–500° C.subl. at 55° C./0.45 torr(d)[Os(CO)3(hfpz)]2189° C.400–550° C.vaporized at 110° C.(e)Ruthenocene194–198225–500° C.yap, pressure 0.01 torr at(a) and (f)85° C.Ru3(CO)12150 dec.150–175° C.vaporized at 50° C.(b)Ru(CO)4(hfb)200–500° C.subl. at 25° C./0.05 torr(c)Ru(tmhd)3210–213250–600° C.subl. at 120° C./0.5 torr(g)Ru(COD)(C3H5)2300° C.vaporized at 75° C.(h)Ru(CO)2(hfac) 55–75° C.400° C.vaporized at 50° C.(i)RuO4 27° C.150–220° C.b.p. = 129° C.highly toxic, (j)Abbreviation:TD = deposition temperature,hfb = hexafluoro-2-butyne,tfa = trifluoroacetate,hfac = hexafluoroacetylacetonate,hfpz = 3,5-bis(trifluoromethyl) pyrazolate,tmhd = 2,2,6,6-tetramethyl-3,5-heptanedionate,C3H5 = allyl andCOD = 1,5-cyclooctadiene.(a) Smart, C. J.; Gulhati, A.; Reynolds, S. K. Mater. Res. Soc. Symp. Proc. 1995, 363, 207.(b) Boyd, E. P.; Ketchumn, D. R.; Deng, H.; Shore, S. G. Chem. Mater. 1997, 9, 1154.(c) Seuzaki, Y.; Gladfelter, W. L.; McCormick, F. B. Chem. Mater. 1993, 5, 1715.(d) Yu, H.-L.; Chi, Y.; Liu, C.-S.; Peng, S.-M.; Lee, G.-H. Chem. Vap. Deposition 2001, 7, 245.(e) Chi, Y.; Yu, H.-L.; Cling, W.-L.; Liu, C.-S.; Chen, Y.-L.; Chou, T.-Y.; Peng, S.-M.; Lee, G.-H. J. Mater. Chem. 2002, 12, 1363.(f) Park, S.-E.; Kim, H.-M.; Kim, K.-B.; Min, S.-H. J. Electrochem. Soc. 2000, 147, 203.(g) Vetrone, J.; Foster, C. M.; Bai, G.-R.; Wang, A.; Patel, J.; Wu, X. J. Mater. Res. 1998, 13, 2281.(h) Barreca, D.; Buchberger, A.; Daolio, S.; Depero, L. E.; Fabrizio, M.; Morandini, F.; Rizzi, G. A.; Sangaletti, L.; Tondello, E. Langmuir 1999, 15, 4537.(i) Lee, F.-J.; Chi, Y.; Hsu, P.-F.; Chou, T.-Y.; Liu, C.-S.; Peng, S.-M.; Lee, G.-H. Chem. Vap. Deposition 2001, 7, 99.(j) Sankar, J.; Sham, T. K.; Puddephatt, R. J. J. Mater. Chem., 1999, 9, 2439.